The present invention relates to a method and device for grinding and separating grain.
A device of this type having two pairs of rolls can be noted from Federal Republic of Germany Patent 709 957. However, the throughput does not remotely satisfy present-day requirements, due to the relatively small screen surface available. There is also the additional factor that the degree of grinding in a mill with only two pairs of rolls can satisfy only modest requirements.
In the past therefore, so-called six-roll mills were predominantly developed and built for the crushing of malt the basic construction of which is known, for instance from Republic of Germany Patent 236 485 and U.S. Pat. No. 4,225,093. These mills are characterized essentially by three pairs of rolls arranged in a triangular configuration and two, mostly multilayer, screen devices, the upper one of which covers approximately the region from below the first pair of rolls to above the second pair or rolls and the lower of which covers approximately the region from below the second to above the last pair of rolls. In most cases, the first and the last pairs of rolls are arranged approximately vertically above each other, while the middle pair of rolls is located on an intermediate plane and laterally staggered by approximately the length of the screen devices.
In this machine design, the output of the mill, which depends generally on the length of the rolls and the size of the screen surface, is determined essentially by the size of the lower screen device over which about 90% of the total amount of product must be moved, while only about 10% of the flour and grits are separated out by the upper screen device and need no longer be passed through the two remaining roll passes.
The screen devices are, as a rule, vibrating screens which are suspended or supported for oscillation and are driven via long connecting rods by an eccentric shaft mounted approximately at the height of the center pair of rolls on the opposite side of the machine housing or even outside the latter. Aside from the uneven loading of the floor caused by the concentration of two pairs of rolls, the eccentric drive and the correspondingly voluminous portion of the housing on one side of the machine, which is undesirable in itself, a reversing moment is produced around the center of gravity of the machine due to the opposing motion of the two vibrating screens at different heights, it being possible for said reversing moment even to be of different size in the event of non-uniformity of the weights of both screens caused, for instance, by product influences. This leads to considerable vibrations of the entire machine, the transmission of which to the base surface can at best be alleviated but not eliminated by suitable vibration insulators such as, for instance, rubber-metal elements. Rather, the machine constantly carries out pitching motions due to the resilience of said vibration insulators which is necessary for their action, so that, for instance, the stationary inlets and outlets for the material can only be connected via flexible elements, such as bellows, etc., to the corresponding feed or discharge devices of the machine. Such vibration insulators and bellows increase the structural expense and result in disadvantages in the important sphere of sanitation; furthermore, they are subject to wear, which is naturally undesirable.